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J-4 project-3.14159265359

Next will be to build the front spars for the horizontal, this morning I printed the horizontal drawing in full size and will start building the tooling to work on.
And yes that is a 99" wide print.
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Lets see if this one stays,
 

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would a lube fitting be a good idea?
Should not be needed as long as the paint on the inside of the tube remains good.
The stainless spars ride in HPDE bushings. They together do not need lubrication. If lower friction were important I would use Delrin for the bearing but it needs to be machined with a thou or two of clearance. The polyethylene is springier as such I make the bushings a light interference fit which will reduce moisture migration. This does not mean I wont grease pack this since if moisture does get in, it will probably not get back out.
That will be determined on final assembly.

I just opened the post with the bad image and the pic appeared. Not sure if it will remain that way, I might have pulled the image directly from the camera which I am finding breaks some form of link that seems to be between my computer and this forum.
 
It is good to see our young one studying.
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Today I bored the ID of the trim actuator to accept some Delrin tube, Installed the tube and bored it to fit the front spar.
This shot is boring the Delrin,
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The spar it turns out will be stepped down in diameter and wall thickness. The innermost section needed to be bored to fit over the middle 1" x .035 section.
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With the inner and middle tubes pressed together and slid into the center trim section.
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A few new pieces, these are the mid span elevator bearing mounts. Made in 304 alloy so they will be maintenance free.
I started with boring the holes the ball bearings will press into, then I made a fixture to mount them centered on my small rotary table to shape the outside.
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Followed with dressing the edges on the flapwheel.
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Working the camera and dressing edges , did not get the shot I wanted. Oh well.
But the parts came out fine.
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These will be slid onto the rear spar and later welded in place.
 

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I have pressed the hing bits onto the rear spar,
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The center of the rear spar,
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The center of the front spar.
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The front spar almost ready to bend into shape.
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A piece of tubing I have been waiting on arrived this morning as such I now have the front spar for the horizontal ready to start forming the sweep into it so I can do the rough building of the structure. The first step once I had it in hand was to ream the ID of the stainless tube since it turns out it was not spot on concentric. Once the carbon tube had a nice snug fit I was able to drill for the retaining through bolts.
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I have allot of cleanup to do on these parts but I have a few years to get that done still, But here are the major trim components.
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Another task I had gotten too was some more drawing on engine parts, this being the intake manifold and exhaust system.
Two renders here.
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First pull on the front spar tube, I am liking it.
I will go back down and do a second pull to get the angle just right.
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Just added a bit more bend to this tube, it is spot on.
Neat thing is when I set it on my iron work bench there is no rock to it as in both sides are clocked the same. That is not always the case.
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Now it is time to make the tooling to build the framework for the horizontal.
 

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Back again, Here is the trim assembly, assembled and it works, well so far.
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At this time it is a power window motor made by Denso. This one is spec'ed for a rear window from an 07 Honda fit. If not real aware these use a worm gear drive so they will not back drive.

The jacksrew is a 16mm ball screw. Probably a bit heavy but absolutely free of play. part of me thinks a 12mm would be fine. Need to see where the plane comes out balance wise.

My design will also allow the installation of a pulley or a sprocket in place of the motor should I prefer a more conventional system.
 
Thanks - I saw that it's a worm drive. We were considering similar, or perhaps a linear actuator on our EAB -12 project. Do you have any reliable info regarding the up/down forces at the stabilizer leading edge? Thinking in terms of required torque on the screw, or axial rating on a linear actuator
.
 
As for loads, no. The force of moving the trim especially with the low friction of a ball screw is fairly low.
The maneuvering loads at the front spar are in the low, hundreds. The rear spar is considerably higher, but still just higher hundreds, not thousands.
I have not truly calculated them on this plane since I believe each time I had in the past I had a pretty low accuracy. On this plane, the airfoil has a pretty low pitching moment, but then there are the flaps. I have run some numbers but my confidence factor is low. I am building with a mild airfoil on this tail, it would not surprise me if I need more lift at low speeds. Easy enough to do but the plane will be down for some rework time.
So far I have only truly had to rework one tail and that was on a very highly modified KR2 I did a full redesign on. We were very early users of the NLF-215 airfoil. I built large span flaps with drooping ailerons center hinged the way the airfoil designer wanted them. Plane was powered with a big VW, a 2350 is I recall. It ran 175+mph WOT,
155 cruise and 30 over the fence. About as good as could be asked for. But when you first slowed it down it ran out of elevator so back home it came. Once the bottom of the stab was reworked the plane was a dream. The engine was frighteningly unreliable, breaking cranks, cracking cases. If you bliped the throttle it would split a prop blade. No clue what power it made but it was generous. Just did not like turning the low revs a prop needed.
A linear actuator would work fine, nice thing is build time is low since they are self packaged.
 
I started the day with making sure the middle elevator hing mounts were spot on. When happy with them I did the first weld and later pressed a bearing in place.
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This afternoon I tackled the first rudder rib. This one is interesting as I want it strong but still under control weight wise. Being the lowest rib at the widest spot on the spar it is quite a triangular structure. The very aft of the fuselage here is 3.5 wide with the rudder spar a bit narrower to take into account the taper in width.
To go after this I chose to make this rib assembly out of box tubing. Not just any box or in this case rectangle tube since this is 3/8 X 1/2 - .012 wall material. I bought this back in the '80s and can not find a source for it anywhere.
Normally I do not even try to weld material this thin in the late afternoon, at least without a shot of Bourbon in me to smooth the nerves.
But here is my first rub, roughed out and just held to the spar with a rubber band. The sides of this have a gentle concave curve to the tubes.
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Charlie, you've been on a tear. I appreciate all the photos because they inspire and give ideas.

I particularly like the elevator hinge arrangement. I was waiting to see how that would work out.
 
I am hoping to get the main structure of the horizontal built the the next day or so. At this point it is kind of down to making a simple jig to hold 3 spars, the third being the elevator. The jig is simply a length of 2X8 with accurately cut grooves in it. I was going to cut the grooves on the mill, but once I placed the rotary table back on it that will be there a short while. So if I get to it, between the chop saw and hand held saws I will make a tool. The spars get clamped into it and I build the structure that will become the horizontal.
I will then assemble the elevator spar with it's hinges which only the middle will mate up at this time. The outer hinge on the horizontal will be built into the composite skin structure that will not be addressed till warm season.
 
As a follow up yesterday I had printed a fresh full size image of the horizontal this time with a depiction of the elevator spar which you can see is not straight. Reasoning being this allows a continuous tube the starts concentric on bearings withe the outer bearings ahead of the spar while still inline with the control horn.
One interesting advantage with this system is when rigging after ground travel or maintenance, the control surface has pins that just insert into bearings, then a threaded retaining bolt is installed. Reset cable tension and you are done.
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Here at the bottom of the rudder, the two bearings are in double shear, the lower bearing on a pin, the upper under a bolt on shear plate with an aluminum axle slid through from the top. Through the center of this is an An3-32 bolt threaded in that can ether be cottered or utilize an MS21042 nut underneath so as to double nut the assembly.
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Two years ago I routed out this 1" MDF tool on a CNC router. Really sweet tool other than my current plan has all the surfaces 3" larger than this was made too. Not to mention the spars have changed. Might find a way to use it but I tend to think it is just some really sweet scrap.
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I am making bunches of pieces for the adjustable pedal assy.
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Charlie, If you were to place this plane into production, you would need the base price to be at least $1,000,000.
 
There are aspects of a one off and an especially complex one that, well I should not use that word here.
The interesting, unseen part is I have four to five times as many hours drawing, and re-drawing this project as well.
The planes I have done in the past I had helpers and since they were drawn on paper, they did not get redrawn most every night.
I am still happy with this project, I am quite sure I would have restored my real J4 in less time but I truly do not want a certified plane and I know I would not like to put $50K+ plus labor into a $20 K airplane.
Had I stuck with rebuilding the J4 38 years ago I would be flying a nice plane now, But the Aeronca Champ came along, then the Luscombe, then the, well Oh well.
 
i cant wait to see the wing stuff. keep it in gear charlie.

The wings are slated for a redraw of some structure. I am thinking of making the fuel tanks removable. If I do so I loose allot of torsional rigidity and I might need to resort to two lift struts. I really do not want to do that. So I would need to increase the stiffness along the tank bay, particularly along the rear spar. I have plenty of time to figure this out.

Today I was able to make good progress on a section of the pedals. The camera's flash chose not to fire at this darker end of the shop, what is shown here are the pedal brackets which ride on plastic bushings, they are inverted at this time simply so I can get at them to weld. These will swing fore and aft altering the pedal geometry on each side. This will also allow for either set of pedals to be stowed when desired. If anything to get the brake pedals away for some feet you do not trust.
These were clamped in place and old jumper cables were used to provide a ground path for welding.
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Once tacked I finished the welds on the table then set some pedal parts in place.
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I should have flipped the image on the right so it would be clocked the same as the other. The image on the left has the bases of the inner and outer pedals, the other image is the bare bracket.
 

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